Optical: systems and elements – Image stabilization – By movable refractive structure
Reexamination Certificate
2003-01-10
2004-09-21
Chang, Audrey (Department: 2872)
Optical: systems and elements
Image stabilization
By movable refractive structure
C359S554000, C359S555000, C359S831000, C359S431000, C359S795000
Reexamination Certificate
active
06795247
ABSTRACT:
BACKGROUND OF THE INVENTION
Optical instruments such as binoculars and telescopes which include an objective lens and an ocular lens have been known. When both the objective lens and the ocular lens are constructed so as to have positive refractive power, an inverted image is formed. In astronomical telescopes this is acceptable. However, in binoculars and terrestrial telescopes, an erecting optical system is placed between the objective lens and the ocular lens in order that the observer can observe an erect image. For example, the erecting optical system often includes an erecting prism, as used in so-called prism binoculars. More particularly, it is common to use a so-called Schmidt erecting prism in the erecting optical system when making compact binoculars.
FIGS.
7
(A) and
7
(B) show an optical system of a prior art optical instrument for observation that uses a Schmidt prism to form an erect image. This optical system is provided with a positive objective lens
110
, an erecting optical system
130
and a positive ocular lens
120
. Moreover, the position “
111
” on the optical axis Z
1
represents the axial position of an image that is formed by the objective lens
110
, and “E. P.” represents the pupil position for observation (eye point).
As shown in FIGS.
7
(A) and
7
(B), the erecting optical system
130
, termed a Schmidt prism, is actually formed of two prisms, namely, a first prism
131
and a second prism
132
which are almost touching but are separated by a small air gap. The first prism
131
has three reflecting, planar surfaces that are active, namely, surfaces
131
A,
131
B, and
131
C. The second prism
132
is a roof prism and has a roof surface
132
C formed of two reflection surfaces that are perpendicular to each other. The second prism
132
has three reflecting, planar surfaces that are active, namely, surfaces
132
A,
132
B and the roof surface
132
C.
In an optical instrument for observation having such an optical system, light emergent from the positive objective lens
110
is first incident upon the surface
131
A of the erecting prism
130
, at which point it is transmitted. Then the light undergoes total internal reflection at the surface
131
B and is directed to the surface
131
C, where it again undergoes total internal reflection. When the light is again incident onto surface
131
B, its incident angle is less than that required for total internal reflection, and so the light is transmitted. Thus, the light is transmitted through surface
131
B and is incident onto the surface
132
A of the second prism
132
.
The light incident upon the second prism
132
undergoes total internal reflection at the surface
132
B, is reflected by a mirror at surface
132
C, and undergoes total internal reflection at surface
132
A, and then is emergent from the surface
132
B and is transmitted to the ocular lens
120
. The inverted image that would normally be formed by the positive objective lens
110
, by the action of the erecting prism
130
, is converted to an erect image. This erect image is then observed by the ocular lens
120
.
When a Schmidt erecting prism
130
is used to erect an image, there is a problem in that ghost light, as will be explained below, may be generated. Namely, as shown in FIGS.
7
(B) and
8
, light
140
that is incident upon the first reflection surface (i.e., the surface
131
B of first prism
131
) at an angle &thgr;1 (
FIG. 8
) that is smaller than the critical angle (the angle required for total internal reflection) is transmitted by the first reflection surface and is emergent from the first prism
131
without being reflected by the first prism
131
. Subsequently, this light then passes through the second prism
132
and the ocular lens
120
and appears as ghost light that deteriorates the quality of the image seen by the observer.
In optical instruments for observation, such as monoculars and binoculars, if a vibration occurs so as to deviate the optical axis of an optical instrument for observation from the viewing direction, an angular deflection of the light rays occurs. Thus, the quality of an observed image may be greatly degraded, especially in the case where the image is observed with a high magnification. Various anti-vibration mechanisms have been proposed for optical instruments in order to prevent the angular deflection of light rays from an observed object due to a vibration. For example, a mechanism has been disclosed which maintains the spatial orientation of an erecting optical system, such as the so-called Schmidt prism
130
, substantially constant despite a vibration or sudden change in the direction of the optical axis of the optical instrument.
However, ghost light is particularly troublesome in an optical system that has been provided with such an anti-vibration or image-stabilizing mechanism. In such an optical system, the spatial orientation of an erecting optical system, such as the Schmidt prism
130
, is maintained constant during a vibration while the objective lens
110
and the ocular lens
120
are rotated by the vibration relative to the Schmidt prism
130
. When the optical system rotates as a result of a vibration or sudden change in the direction of the optical axis of the optical instrument, the objective lens
110
receives light that originally was outside the effective diameter of the objective lens
110
. Some of this light may not undergo total internal reflection in the Schmidt prism, such as at surface
132
A, and will produce ghost light that will degrade the quality of the observed image.
BRIEF SUMMARY OF THE INVENTION
The present invention relates to an optical instrument for observation which uses an inverting optical system (erecting system) for forming an erect image, and more particularly, relates to an optical instrument for observation such as binoculars or a telescope, etc., that is provided with an anti-vibration mechanism. In particular, the present invention relates to an optical instrument for observation which can prevent the occurrence of ghost light.
REFERENCES:
patent: 2456521 (1948-12-01), Maxwell
patent: 4235506 (1980-11-01), Saito et al.
patent: 5166820 (1992-11-01), Fujita
patent: 6476983 (2002-11-01), Kodama et al.
patent: H6-250100 (1994-09-01), None
Arnold Bruce Y.
Arnold International
Chang Audrey
Fuji Photo Optical Co., Ltd.
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